Large pieces of commercial equipment often have fixed components in close proximity with moving components. In a gas turbine, for example, a compressor includes multiple stages of rotating blades in close proximity with stationary vanes. Ambient air enters the compressor, and the rotating blades and stationary vanes progressively impart kinetic energy to the working fluid (air) to increase the pressure of the working fluid and bring it to a highly energized state. The compressed working fluid flows to one or more combustors which mix fuel with the compressed working fluid and ignite the mixture to produce combustion gases having a high temperature and pressure. The combustion gases flow through alternating stages of rotating blades or buckets and fixed blades or nozzles in the turbine. The rotating blades or buckets are attached to a rotor, and expansion of the combustion gases as they flow through the turbine stages cause the buckets, and thus the rotor, to rotate to produce work.
The clearance between the rotating and stationary components in the compressor and turbine is an important design and operational consideration that balances efficiency and performance on the one hand with manufacturing and maintenance costs on the other hand. For example, reducing the clearance between the buckets and the static shroud or casing in the turbine generally improves the efficiency and performance of the turbine by reducing the amount of combustion gases that bypass the turbine buckets. However, reduced clearances may also result in additional manufacturing costs to achieve the reduced clearances and increased maintenance costs attributed to increased rubbing, friction, or impact between the rotating and stationary components.
The clearances between rotating and stationary components are often checked during assembly and periodically after operations to ensure that the design clearances are maintained and the components are properly aligned. During assembly, the rotating and stationary components may be readily accessible to verify clearances. However, once assembled, the rotating and stationary components may not readily accessible. As a result, extended shutdown periods to allow for time-consuming disassembly of the components may be necessary to gain direct access to the clearances to be measured. Alternately, the clearances may be indirectly measured by measuring adjacent components. However, indirect measurement of the clearances introduces error in the measurements, and the introduced errors may be significant in comparison to the allowable or desired clearances. Therefore, a device for directly measuring clearances between rotating and stationary components in assembled equipment would be desirable.